Pfizer says its drug is best hope for Alzheimer's

But Siemers told Reuters the shorter trials enabled Lilly to get solanezumab into late-stage trials far more quickly and at far less expense, hopefully without compromising future results.

Many investors consider bapineuzumab and Lilly's rival injectable drug long shots because they treat patients that already have developed mild to moderate symptoms, such as memory loss and inability to perform daily chores, and therefore may have suffered irreversible damage to neurons and brain tissue.

Dolsten cautioned that Alzheimer's patients would probably need to be treated at earlier stages of the disease to produce the most beneficial results, a prospect he sees likely within the next five years.

Pfizer is counting on newer drugs to deliver revenue needed to offset plunging sales of its Lipitor cholesterol fighter, which has faced cheaper generics since November.

They include Prevnar 13, an improved form of its Prevnar vaccine to prevent infections with streptococcus bacteria. The U.S. Food and Drug Administration in December approved its use for adults aged 50 and older, greatly widening the market for the product, which had been approved only in children.

Dolsten said Pfizer expects data by next year from late-stage trials testing whether Prevnar 13 prevents pneumonia in adults. The $3.3 billion-a-year vaccine could get a big commercial boost if the trials succeed, especially in preventing pneumonia among the elderly, he said.

The world's biggest drugmaker also has high hopes for tofacitinib, an experimental pill that treats rheumatoid arthritis through a new approach and is awaiting U.S. approval.

The FDA is slated to decide on tofacitinib by August, but Dolsten said an FDA advisory panel of outside experts is likely to weigh the drug's safety and effectiveness beforehand.

"We expect a dialogue about how this drug will be used," Dolsten said, given its new mechanism of action. It is the first in an emerging class of drugs known as JAK inhibitors that block a protein associated with inflammation.

The research chief also expressed confidence Pfizer will eventually develop an anti-smoking vaccine and important new treatments for cardiovascular disease and diabetes.

Last year, Pfizer said it would slash its annual research budget by as much as $2 billion in order to deliver on earnings goals.